KR20210076911A - Control method of light modulator - Google Patents

Abstract

An apparatus for an extreme ultraviolet (EUV) light source, comprising: a light modulation system comprising an electro-optic material, the light modulation system configured to receive a pulsed light beam comprising a plurality of light pulses separated in time from each other; and a second electric pulse is applied to the electro-optic material while a second light pulse is incident on the electro-optic modulator, such that a first electric pulse is applied to the electro-optic material while the first light pulse is incident on the electro-optic material. control the power source such that after the first light pulse is incident on the electro-optic material an intermediate electric pulse is applied to the electro-optic material before the second light pulse is incident on the electro-optic material a configured control system.

Description

Control method of light modulator

Cross-referencing of related applications

This application claims priority to US Application No. 62/747,518, filed on October 18, 2018, which is incorporated herein by reference in its entirety.

The present disclosure relates to control of an optical modulator. For example, light leakage of the light modulator may be controlled. The light modulator may be an extreme ultraviolet (EUV) light source and/or part of a lithography system.

Extreme ultraviolet ("EUV") light, for example, having a wavelength of 100 nanometers (nm) or less (also sometimes called soft x-rays), and, for example, 20 nm or less, 5-20 nm, Alternatively, electromagnetic radiation, including light with a wavelength of 13 to 14 nm, may be used in a photolithography process to create microscopic features by initiating polymerization in a resist layer of a substrate, eg, a silicon wafer.

Methods for generating EUV light include, but are not necessarily limited to, converting a material containing an element such as, for example, xenon, lithium, or tin into a bright line in the EUV range in a plasma state. In one of these methods, the required plasma, often referred to as a laser-generated plasma (“LPP”), is an amplified light beam, which may be referred to as a drive laser, into a target material, e.g., a droplet, plate, tape, stream of material. , or by irradiating the target material in cluster form. In this process, plasma is typically generated in a closed vessel, such as a vacuum chamber, and monitored using various types of metrology equipment.

In one general aspect, there is provided an apparatus for an extreme ultraviolet (EUV) light source, the apparatus comprising: a light modulation system comprising an electro-optic material, the light modulation system comprising a pulsed light beam comprising a plurality of light pulses separated in time from each other configured to receive -; and a second electric pulse is applied to the electro-optic material while a second light pulse is incident on the electro-optic material, such that a first electric pulse is applied to the electro-optic material while the first light pulse is incident on the electro-optic modulator. control the power source such that after the first light pulse is incident on the electro-optic material an intermediate electric pulse is applied to the electro-optic material before the second light pulse is incident on the electro-optic material a configured control system.

Implementations may include one or more of the following features. A first electrical pulse applied to the electro-optic material may cause a physical effect in the electro-optic material, and the physical effect may be present in the electro-optic material when an intermediate electrical pulse is applied to the electro-optic material. Physical effects may include electro-optic materials and/or mechanical strain. Applying intermediate electrical pulses to the electro-optic material may reduce the physical effect.

The first light pulse and the second light pulse may be continuous light pulses in a pulsed light beam.

The control system may be configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse.

The electro-optic material may include a semiconductor.

The electro-optic material may include an insulator.

The electro-optic material may include electro-optic crystals.

The device may include at least one polarization-based optical element.

In another general aspect, an apparatus for forming light pulses includes a light modulation system comprising an electro-optic material, the light modulation system configured to transmit light in an ON state and block light in an OFF state, the light modulation system comprising: The light modulation system is configured to receive a pulsed light beam comprising at least a first light pulse and a second light pulse separated from each other in time. A control system may be coupled to the voltage source, the control system causing the voltage source to cause a first voltage pulse to the electro-optic modulator while the first light pulse is incident on the electro-optic modulator (the first voltage pulse turns the electro-optic modulator ON to generate a first shaping light pulse by applying a first shaping light pulse; to apply an intermediate voltage pulse to the electro-optic material; and generate a second shaping light pulse by applying a second electrical pulse to the electro-optic material after applying the first voltage pulse and the intermediate voltage pulse and while the second light pulse is incident on the electro-optic material. The second voltage pulse is configured to turn the electro-optic modulator into an ON state, and a characteristic of the second forming light pulse is controlled by applying an intermediate voltage pulse to the electro-optic material.

Implementations may include one or more of the following features. The second forming light pulse may include a pedestal portion and a main portion, wherein the property of the second forming light pulse is a characteristic of the pedestal such that the property of the pedestal portion is controlled by applying an intermediate voltage pulse to the electro-optic material. may include. The pedestal portion and the main portion may be continuous in time. A characteristic of the pedestal portion may be a temporal duration, maximum intensity, and/or average intensity of the pedestal portion.

Applying an intermediate voltage pulse to the electro-optic material may alter the optical leakage light transmitted through the light modulation system in the OFF state. Applying an intermediate voltage pulse to the electro-optic material may reduce optical leakage light transmitted through the light modulation system in the OFF state.

In some implementations, a first voltage pulse is applied to the electro-optic material at a first time by the control system, and an intermediate voltage pulse is applied to the electro-optic material at a second time that is after the first time by the control system; The second time and the first time are temporally separated by a delay time, and the control system is further configured to adjust the delay time to control a characteristic of the second forming light pulse.

The control system may be further configured to control at least one of an amplitude, a temporal duration, and a phase of the intermediate voltage pulse.

The control system may be further configured to receive an indication of a measured characteristic of the pedestal portion and to adjust a characteristic of the intermediate electrical pulse based on the received indication.

The control system may be further configured to receive an indication of an amount of extreme ultraviolet (EUV) light generated by the plasma, and to adjust a characteristic of the intermediate voltage pulse based on the indication of an amount of the received EUV light. A control system configured to adjust a characteristic of the intermediate voltage pulse comprises: configured to adjust an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a second time, wherein the second time is the time at which the intermediate voltage pulse is applied to the electro-optic material.

In another general aspect, a method of adjusting a characteristic of an optical pulse comprises: forming a first optical pulse by applying a first voltage pulse to an electro-optical material of a light modulation system while light is incident on the optical modulation system; applying an intermediate voltage pulse to the electro-optic material after applying the first voltage pulse; and forming a second light pulse by applying a second voltage pulse to the electro-optic material after the first voltage pulse and the intermediate voltage pulse and while the light is incident on the electro-optic material. The properties of the light pulses are adjusted based on the application of the intermediate voltage pulses.

Implementations may include one or more of the following features. the first light pulse may be amplified to form an amplified first light pulse; an indication of an amount of extreme ultraviolet (EUV) light emitted from the plasma generated by interacting the amplified first light pulse with the target material may be received; At least one characteristic of the intermediate voltage pulse may be determined based on the received indication of an amount of EUV light emitted from the plasma. The at least one characteristic of the intermediate voltage pulse may include a time delay after application of the first voltage pulse, wherein determining the at least one characteristic of the intermediate voltage pulse is based on a received indication of an amount of EUV light emitted from the plasma. determining a time delay. The at least one characteristic of the intermediate voltage pulse may include an amplitude and/or duration of the intermediate voltage pulse, wherein determining the at least one characteristic of the intermediate voltage pulse comprises determining the amplitude and/or duration of the intermediate voltage pulse. may include

The second light pulse includes a pedestal portion and a main portion, and a characteristic of the pedestal portion is adjusted based on application of the intermediate voltage pulse. The pedestal portion may be temporally continuous with the main portion.

In another general aspect, an extreme ultraviolet (EUV) light source comprises a container; a target material supply device configured to couple to the container; a light modulation system configured to be positioned to receive a pulsed light beam, the light modulation system comprising an electro-optic material; and a control system coupled to the voltage source, the control system causing the voltage source to apply a plurality of forming voltage pulses to the electro-optic material, each of the plurality of forming voltage pulses being applied to the electro-optic material at a different time; and cause the voltage source to apply at least one intermediate voltage pulse to the electro-optic material, wherein the at least one intermediate voltage pulse is applied to the electro-optic material between two pulses of the plurality of forming voltage pulses.

Implementations may include one or more of the following features. The target material supply apparatus may be configured to provide a plurality of target material droplets to the target area within the container, the target material droplets arriving at the target area at a target delivery rate, and wherein the control system is configured to provide a formation rate dependent on the target delivery rate. A forming voltage pulse is applied to the electro-optic material.

The characteristics of the intermediate electrical pulse may include amplitude and/or phase, and the control system causes the voltage source to access the stored amplitude and/or phase in relation to the rate of formation, and causes the voltage source to have the intermediate voltage with the accessed amplitude and/or phase. and may be further configured to generate a pulse. The control system may be further configured to control a time delay between application of one of the forming voltage pulses and one of the intermediate voltage pulses.

The EUV light source may also include an optical amplifier. A light pulse may be formed whenever a forming voltage pulse is applied to the electro-optic material; The formed optical pulse may be amplified by an optical amplifier to form an amplified optical pulse; The control system may be further configured to be coupled to a metrology system configured to measure an amount of EUV light generated by the plasma within the vessel, wherein the plasma may be formed by irradiating a target material with the formed amplified light pulses, the control system comprising: be configured to receive a measured amount of EUV light from the metrology system; The control system may be configured to change one or more characteristics of the intermediate voltage pulse based on the measured amount of EUV light. One or more characteristics of the intermediate voltage pulse may include an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a delay time after application of a most recent forming voltage pulse.

Implementations of any of the techniques described above may include an EUV light source, system, method, process, device, or apparatus. The details of one or more implementations are set forth in the accompanying drawings and the detailed description below. Other features will become apparent from the detailed description, drawings and claims.

1 is a block diagram of an example of an EUV lithography system.
2A is a block diagram of an example of a modulation system.
2B is an exemplary diagram of an example of a light pulse.
FIG. 2C is an exemplary diagram of an example of a modulated light pulse formed from the light pulse of FIG. 2B.
3A is an illustrative diagram of an example of a light beam as a function of time.
3B is an illustrative diagram of an example of an electrical signal as a function of time.
4 is a flowchart of an example of a process for controlling the characteristics of an irradiating light pulse.
5 and 6 are block diagrams of an example of a lithographic apparatus.
7 is a block diagram of an example of an EUV light source.

Techniques for controlling light leakage in electro-optic modulators are described. An electro-optic modulator is used to modulate the original light beam to form a modulated light pulse. The electro-optic modulator comprises an electro-optic material. An electrical signal (eg, a voltage pulse having a finite duration) is applied to the electro-optic material to change the refractive index of the electro-optic material such that the original light beam is modulated to form a modulated light pulse. After application of the electrical signal, an intermediate electrical signal is applied to the electro-optic material. As will be described in detail below, applying an intermediate electrical signal to the electro-optic material can control the light leakage of the electro-optic modulator. The intermediate electrical signal dampens, changes, or controls the sound waves produced by the electrical signal. Controlling the sound waves also controls the amount of light leakage of the electro-optic modulator, so that the properties of the subsequently formed (or later formed) modulated light pulses can be controlled.

1 , a block diagram of a system 100 is shown. System 100 is an example of an EUV lithography system. System 100 includes an EUV light source 101 that provides EUV light 196 to a lithographic apparatus 195 . A lithographic apparatus 195 exposes a wafer (eg, a silicon wafer) with EUV light 196 to form electronic features on the wafer. EUV light 196 is emitted from plasma 197 formed by irradiating a target material within target 118 with an irradiating light pulse 108 . The target material is any material that emits EUV light in a plasma state (eg, tin).

The EUV light source 101 includes a light pulse generation system 104 , which generates an amplified light pulse 108 from the modulated light pulse 107 . The optical pulse generation system 104 may be, for example, a pulsed (eg, Q switched) or continuous wave carbon dioxide (CO ₂ ) laser or a solid state laser (eg, a Nd:YAG laser or an erbium doped fiber). and a light source 105 which may be a (Er:glass) laser. The light source 105 produces a light beam 106 (or light beam 106 ), which may be a series of light pulses or a continuous light beam. Light source 105 emits light beam 106 onto path 111 towards modulation system 120 comprising electro-optic material 122 . The electro-optic material 122 is on the path 111 , and the light beam 106 is incident on the electro-optic material 122 .

Modulation system 120 is an electro-optic modulator that modulates light beam 106 based on electro-optic effects. The electro-optic effect describes the change in the refractive index of the electro-optic material 122 caused by the application of a direct current (DC) or low frequency electric field 124 generated by the power source 123 . The power source 123 may be, for example, a voltage source, a function generator, or a power source. By controlling the electro-optic effect of the electro-optic material 122 while the light beam 106 is incident on the electro-optic material 122 , the modulation system 120 modulates the phase, polarization, or amplitude of the light beam 106 to form a pulse 107 .

The electric field 124 may be used to control whether the modulation system 120 transmits light. The electric field 124 may be used to control the electro-optic material 122 such that only one or a plurality of specific portions of the light beam 106 pass through the electro-optic material 122 . In this way, the modulation system 120 forms a pulse 107 from a portion of the light beam 106 .

Optical pulse generation system 104 also includes one or more optical amplifiers 130 , each of which includes a gain medium 132 on path 111 . Gain medium 132 receives energy through pumping and provides this energy in pulses 107 to amplify pulses 107 into amplifying light pulses or irradiating light pulses 108 . The amount of amplification of the pulse 107 is determined by the gain of the amplifier 130 and the gain medium 132 . Gain is the increment or coefficient of energy that amplifier 130 provides to the input light beam.

Pulse 108 propagates on path 111 towards a vacuum vessel containing target 118 . Pulse 108 and target 118 interact at target area 115 within vacuum vessel 180 , whereby at least a portion of the target material within target 118 emits EUV light 196 . converted to plasma 197 .

Applying an electric field 124 to the electro-optic material 122 creates a sound wave within the material 122 . The sound wave creates a strain in the material 122 and may persist after the electric field 124 is no longer applied to the material 5 and/or after the properties of the electric field 124 have changed. The deformation induced by the sound waves changes the refractive index of the material 122 even during times when the refractive index of the material 122 is not expected to change. This change in refractive index can lead to light leakage. Light leakage is the light passing through the modulator 120 when the modulation system 120 is in a state in which the light should not pass through the modulation system 120 . As described below, an electric field 124 is applied to the material 122 to mitigate and/or control light leakage by mitigating and/or controlling residual acoustic waves within the material 122 (eg, pulses). ) is included.

EUV light source 101 also includes metrology system 182 positioned relative to target area 115 . Metrology system 182 includes one or more sensors 184 configured to sense EUV light 196 . Metrology system 182 generates an indication of the amount of EUV light 196 within vacuum chamber 180 (eg, in target area 115 ). Metrology system 182 provides data indicative of the amount of EUV light measured to control system 175 via communication link 183 .

In some implementations, metrology system 182 also includes a light sensing system 185 that includes one or more optical sensors configured to measure characteristics of the pulses 107 and/or the amplified pulses 108 . The light sensing system 185 is configured such that the monitoring system 185 can determine the characteristics of the pulses 107 and/or the amplified pulses 108 (eg, characteristics of the pedestal portion) of the pulses 107 and/or. or any sensor capable of detecting one or more wavelengths of the pulse 108 . In the example of FIG. 1 , the light sensing system 185 is part of the metrology system 182 , however, the light sensing system 185 may be separate from the metrology system 182 . For example, the optical sensing system 185 may be positioned between the modulation system 120 and the optical amplifier 130 to receive a sample of the optical pulses 107 . The light sensing system 185 may also provide data related to the measurement of the light pulses 107 and/or pulses 108 to the control system 175 . In some implementations, information from EUV sensor 184 and/or light sensing system 185 is used by control system 175 to set and/or change parameters of electric field 124 .

In addition to receiving data from metrology system 182 , control system 175 may communicate data and/or data with pulse generation system 104 and/or any components of pulse generation system 104 via communication interface 176 . or exchange information. For example, in some implementations, the control system 175 can provide a trigger signal to operate the modulation system 120 and/or the light source 105 . In another example, the control system 175 receives the measured amount of EUV light from the EUV sensor 184 for many interactions between the instance of the irradiating light pulse 108 and the instance of the target 118 to generate an electric field 124 . It is possible to determine which of the many possible settings of a particular parameter or characteristic of α produces the highest amount of EUV light. In another example, the control system 175 provides data and/or information to the power source 123 that generates the electric field 124 . In this embodiment, data provided by control system 175 determines various characteristics of electric field 124 , such as, for example, the amplitude and/or time delay between two pulses of electric field 124 .

The control system 175 includes an electronic processor 177 , an electronic storage 178 , and an input/output (I/O) interface 179 . Electronic processor 177 includes one or more processors suitable for the execution of computer programs, such as general or special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, electronic processors receive instructions and data from read-only memory, random access memory, or both. Electronic processor 177 may be any type of electronic processor.

The electronic storage device 178 may be a volatile memory such as RAM or a non-volatile memory. In some implementations, electronic storage 178 includes non-volatile and volatile portions or components. The electronic storage 178 may store data and information used in the operation of the control system 175 and/or components of the control system 175 .

Electronic storage 178 may store instructions, such as computer programs, that, when executed, cause processor 177 to communicate with components within control system 175 , modulation system 120 , and/or light source 105 . You can also save it. For example, in implementations where light source 105 is a pulsed light source, the instructions may be instructions that cause electronic processor 177 to generate a signal, which in turn causes light source 105 to emit light pulses.

I/O interface 179 enables control system 175 to receive data and signals and/or transmit data and signals to operators, modulation system 120, and/or light sources, and/or other electronic devices. Any type of electronic interface that makes it possible to provide an automated process running on it. For example, I/O interface 179 may include one or more of a visual display, a keyboard, and a communication interface.

2A is a block diagram of a modulation system 220 . This modulation system 220 is an example of an implementation of the modulation system 120 (FIG. 1). Modulation system 220 includes electro-optic material 122 , which, in the implementation shown in FIG. 2A , is positioned between electrodes 223a and 223b. Electrodes 223a, 223b are controllable to form an electric field between electrodes 223a, 223b. For example, by the control system 175, the voltage source 223 provides a voltage signal 214 to the electrode 223b such that the electrode 223b is maintained at a different voltage than the electrode 223a, and thus the electro-optic material ( 122) creates an electric field or potential difference (V).

Further, the modulation system 220 may include multiple instances of the electro-optic material 122 . For example, modulation system 220 may include two electro-optic materials 122 , three electro-optic materials 122 , or any number suitable for use may be disposed on beam path 111 . can Each instance of the electro-optic material 122 also includes a respective electrode 223a , 223b controllable to apply an electric field to the electro-optic material 122 . In implementations that include multiple instances of electro-optic material 122 , the electric field applied to each electro-optic material 122 may be the same, or at least some of the electro-optical fields may be different. The electro-optic materials 122 may be controlled by the control system 175 as a group, or the various electric fields may be individually controllable by each instance of the control system 175 .

The modulation system 220 also includes one or more polarization-based optical elements 224 . In the example of FIG. 2A only one polarization-based optical element 224 is shown. However, in other implementations, additional polarization-based optical elements 224 may be included. For example, the second polarization-based optical element 224 may be on one side of the modulation system 220 receiving the light beam 106 . Also, although the polarization-based optical element 224 is shown as physically separate from the electro-optic material 122 , other implementations are possible. For example, the polarization-based optical element 224 may be a film formed on the electro-optic material 122 such that the optical element 224 and the electro-optic material 122 are in contact with each other.

Polarization-based optical element 224 is any optical element that interacts with light based on the polarization state of the light. For example, the polarization-based optical element 224 may be a linear polarizer that transmits horizontally polarized light, blocks vertically polarized light, or vice versa. The polarization-based optical element 224 may be a polarizing beam splitter that transmits horizontally polarized light and reflects vertically polarized light. The polarization-based optical element 224 may be an optical element that absorbs all light except light having a particular polarization state. In some implementations, the polarization-based optical element 224 can include a quarter wave plate. At least one polarization-based optical element 224 is positioned to receive light passing through the electro-optic material 122 and to direct light of a particular polarization state onto the beam path 111 .

As described above, one electro-optic material 122 and one polarization-based optical element 224 are shown in FIG. 2 , however either or both of these components are in series with each other on the beam path 111 . and may be included in the modulation system 120 . For example, the modulation system may include three polarization-based optical elements 224 and two electro-optic materials 122 in series on a beam path 111 , each of which has three between two of the polarization-based optical elements 224 .

The electro-optic material 122 may be any material that transmits one or more wavelengths of the light beam 106 . For implementations where light beam 106 includes light at a wavelength of 10.6 microns (μm), material 122 may be, for example, cadmium zinc telluride (CdZnTe or CZT), cadmium telluride (CdTe), zinc telluride (ZnTe), and/or gallium arsenide (GaAs). Different materials may be used at different wavelengths. For example, material 122 may be monopotassium phosphate (KDP), ammonium dihydrogen phosphate (ADP), quartz, cuprous chloride (CuCl), zinc sulfide (ZnS), zinc selenide (ZnSe), lithium niobate (LiNbO ₃ ), gallium phosphide (GaP), lithium tantalate (LiTaO ₃ ), or barium titanate (BaTiO ₃ ). Other materials that transmit one or more wavelengths of the light beam 106 and exhibit birefringence in response to application of an external force may also be used as the material 122 . For example, quartz may be used as material 122 .

The electro-optic material 122 also exhibits anisotropy. In materials exhibiting anisotropy, the properties of the material (eg, refractive index) are spatially non-uniform. Accordingly, the properties of the material 122 may be modulated in a specific direction or along specific directions by application of a controllable external force, such as a potential difference (V). For example, the refractive indices of different polarization components of light propagating through material 122 may be controlled through application of an external force. Thus, the polarization state of the light passing through the material 122 can be controlled by controlling the potential difference (V) between the electrodes 223a and 223b.

Under ideal operation, modulation system 220 will only operate if, by a potential difference (V) applied to material 122 , the polarization state of light passing through material 122 matches the polarization state of polarization-based optical element 224 . transmit light. For example, the polarization-based optical element 224 is a linear polarizer positioned to transmit horizontally polarized light onto the beam path 111 , and the light beam 106 is initially incident on the material 122 vertically. When polarized, only when a potential difference (V) applied to material 122 changes the polarization state of light beam 106 such that light beam 106 is horizontally polarized before interacting with polarization-based optical element 224 . A pulse 107 is formed.

The modulation system 220 is considered to be in the ON state whenever the modulation system 220 is intentionally controlled to transmit light. For example, if the applied potential difference (V) is a polarization state in which the polarization state of the light beam 106 matches that of the polarization-based optical element 224, then the light modulation system 220 is considered to be in the ON state, A pulse 107 is formed. When the applied potential difference V is the polarization state where the polarization state of the light beam 106 is expected to be perpendicular to the polarization-based optical element 224 , the light modulation system 220 is in the OFF state. Under ideal conditions, the light beam 106 does not pass through the modulation system 120 when the light modulation system 220 is in the OFF state.

However, applying a potential difference (V) to the material 122 causes sound waves to propagate within the material 122 . These sound waves may persist even after the potential difference V is removed from the material 122 . The sound waves also cause deformations that change the optical properties of the material 122 , allowing incident light to pass through the modulation system 220 (as light leakage) even when no potential difference V is applied. Thus, in actual operation, the modulation system 220 is

The polarization-based optical element 224 will transmit spurious light (light leakage) even if the polarization state of the optical element 224 is a polarization state where light incident on the material 122 should not pass through the modulation system 220 . can For example, a light leak exists just before an irradiating light pulse is formed, and the light leak forms a pedestal portion on the illuminating light pulse.

Referring also to FIGS. 2B and 2C , an example of an example optical pulse 206 ( FIG. 2B ) and an example of a modulated optical pulse 207 formed from the optical pulse 206 are shown. Pulse 207 includes a pedestal portion 225 and a main portion 268 . FIG. 2B shows the intensity of pulse 206 as a function of time, and FIG. 2C shows the intensity of pulse 207 as a function of time.

Pulse 206 has a time profile (intensity versus time) that is approximately Gaussian. Pulse 206 interacts with modulation system 220 to form pulse 207 . The control system 175 controls the modulation system 220 to select or extract a particular portion 267 of the pulse 206 . In the example of FIG. 2B , at time t=ta, modulation system 220 is set to transmit light, and at time t=tb, modulation system 220 is set to block light. In other words, light modulation system 220 is intended to transmit only light within portion 267 (light in pulse 206 between time ta and time tb). For example, the control system 175 can control the light at time ta by applying a voltage signal 214 such that light passing through the electro-optic material 122 has a polarization that matches the polarization of the polarization-based optical element 224 . The modulation system 220 can be controlled to transmit Modulation system 220 may be controlled to stop transmission of light at time tb by removing voltage signal 214 .

However, due to sound waves in the electro-optic material 122 (or other disturbances such as unexpected movement of the polarization-based optical element 224 ), light leakage occurs before time ta and/or after time tb. ) can penetrate. In the example of FIG. 2B , leaking light 266 is a light leak that occurs just before time ta. Leaked light 266 passes through modulation module 120 just before portion 267 .

Referring to FIG. 2C , the leaking light 266 forms a pedestal portion 225 . In the illustrated example, pedestal portion 225 occurs during the window indicated at 221 , and pedestal portion 225 occurs earlier in time than the remainder of pulse 207 . The portion of the light pulse 207 that is not the pedestal portion 225 is referred to as the main portion 268 . Both the pedestal portion 225 and the main portion 268 are part of the light pulse 207 , and the pedestal portion 225 is temporally connected to the main portion 268 . In other words, there is no light-free period between the pedestal portion 225 and the main portion 268 .

The pedestal portion 225 has a different temporal profile (intensity as a function of time) than the main portion 268 . For example, the average intensity and maximum intensity and optical energy of the pedestal portion 225 is less than the average intensity and maximum intensity and optical energy of the main portion 268 . Also, the shape of the pedestal portion 225 is different from the shape of the main portion 268 . Also. The properties (eg, intensity, temporal profile, and/or duration) of the pedestal portion 225 differ from those of the initial portion of the pulse formed without any light leakage.

The modulated pulse 207 is amplified by the amplifier 130 to form an amplified pulse 108 , which propagates to the target area 115 . The amplified pulse 208 includes a pedestal portion 225 and a main portion 268 , each portion 225 , 268 of the amplified pulse 208 having a greater intensity than a corresponding portion of the modulated pulse 207 . has In the example of FIG. 2C , the pedestal portion 225 occurs before the main portion 268 and reaches the target 118 before the main portion 268 . In some implementations, the main portion 268 has sufficient intensity or energy to transform at least a portion of the target material in the target 118 into a plasma that emits EUV light. The pedestal portion 225 does not have as much energy as the main portion 268 , and may or may not have sufficient energy to convert the target material into a plasma. However, light from the pedestal portion 225 may be reflected off the target 118 , may evaporate material from the surface of the target 118 , and/or may destroy a portion of the target 118 . Pedestal portion 225 may interfere with plasma formation by altering target 118 before main portion 268 reaches target 118 , and/or undesirable reflections propagating back on path 111 . may cause

On the other hand, pedestal portion 225 may condition target 118 such that its properties (eg, density, shape, and/or size) are more favorable for plasma generation. Accordingly, it is desirable to control the amount of light within the pedestal portion 225 by controlling the amount of light leakage. Control system 175 uses an intermediate electrical signal applied to electro-optic material 122 prior to formation of pulse 207 to control the amount of light leakage (in this example leakage light 266 ).

The pulse 207 described with respect to FIGS. 2B and 2C is provided as an example of a modulated light pulse 207 . Pulse 207 may take other forms. For example, the leaking light 266 may occur before time ta such that the pedestal portion 225 is separated from the main portion 268 . In these implementations, there is a light-free period between the pedestal portion 225 and the main portion 268 . Also, the leaking light 266 may occur after time tb such that the pedestal portion 225 occurs after the main portion 268 . In these implementations, the pedestal portion 225 reaches the target area 115 after the main portion 268 . In some implementations, the leaking light 266 occurs before time ta and after time tb such that pedestal portions 225 are present on both sides of main portion 268 .

3A is a plot of the intensity of the light beam 306 as a function of time. 3B is a plot of the voltage of electrical signal 324 as a function of time. 3a and 3b the same time scale is used. Electrical signal 324 is an example of an electrical signal that may be generated by a function generator controlled by control system 175 and applied to electro-optic material 122 ( FIGS. 1 and 2A ). Electrical signal 324 is described for modulation system 220 (FIG. 2A). Light beam 306 is an example of an optical beam (or light beam) that may be incident on electro-optic material 122 .

The light beam 306 includes two initial optical light pulses, a first initial light pulse 306_1 and a second initial light pulse 306_2 incident on the material 122 . A first initial light pulse 306_1 is incident on the material 122 before a second initial light pulse 306_2 is incident on the material 122 . The first optical pulse 306_1 and the second optical pulse 306_2 are separate optical pulses separated from each other in time. The light beam 306 may include light pulses other than the initial light pulses 306_1 and 306_2.

Electrical signal 324 includes a first electrical pulse 325a_1 applied to material 122 starting at time t1 , and a second electrical pulse 325a_2 applied to material 122 starting at time t2 . Electrical pulses 325a_1 and 325a_2 are voltage pulses each having an amplitude of A volts for finite temporal durations 331_1 and 331_2. Thus, application of electrical pulses 325a_1 and 325a_2 results in a voltage of A applied to material 122 for temporal durations 331_1 and 331_2, respectively.

Voltage A is a voltage sufficient to turn on modulation system 220 . Thus, light incident on material 122 is transmitted through light modulation system 220 while electrical pulses 325a_1 and 325a_2 are applied to material 122 . After the electrical pulses 325a_1 and 325a_2 have ended, the modulation system 220 returns to the OFF state.

The temporal durations 331_1 and 331_2 may be the same or different. In the implementation of FIG. 3B , the first and second electrical pulses 325a_1 and 325a_2 have the same voltage amplitude (A). However, in other implementations, electrical pulses 325a_1 and 325a_2 have different voltage amplitudes, and both electrical pulses 325a_1 and 325a_2 have a voltage sufficient to transition modulation system 220 to an ON state.

Electrical signal 324 also includes an intermediate electrical pulse 325b_1 applied to material 122 at time ti. Time ti occurs after time t1 and before time t2. The time ti is separated from the time at which the first electrical pulse 325a_1 ends by a delay time 330 . The intermediate electrical pulse 325b_1 has an amplitude B of temporal duration or width 332 .

At time zero, modulation system 220 is in the OFF state. Application of the first electrical pulse 325a_1 at time t1 transitions the modulation system 220 to the ON state. At time t1 , a first light pulse 306_1 is incident on material 122 . The temporal duration of the first electric pulse 325a_1 is shorter than the temporal duration of the first optical pulse 306_1 . Accordingly, only the portion of the first optical pulse 306_1 incident on the material 122 during the duration 331_1 passes through the material 122 . A portion of the first light pulse 306_1 passing through the material forms a modulated light pulse (eg, modulated light pulse 207 in FIG. 2C ). Applying a first electrical pulse 325a_1 to the material 122 generates a sound wave within the material 122 . These sound waves cause deformation to change the optical properties of the material 122 . The sound wave continues to propagate in the material 122 after the first electrical signal 325a_1 has ended and no voltage is applied to the material 122 . The sound wave caused by the application of the first electrical signal 325a_1 occurs when the second optical pulse 306_2 is incident on the material 122 , but before the second electrical signal 325a_2 is applied to the material 122 . may exist. In this situation, light may pass through modulation system 220 even when modulation system 220 is in the OFF state. This light is a light leak and later forms a pedestal on the light pulses formed by the modulation system 220 .

4 is a flow diagram of an example of a process 400 for controlling the characteristics of an irradiating light pulse. The irradiating light pulse may include a pedestal portion. Process 400 includes EUV light source 101 and control system 175 (FIG. 1), modulation system 220 (FIG. 2A), light beam 306 (FIG. 3A), and electrical signal 324 (FIG. 3B). is explained about. However, process 400 may be performed by other EUV light sources, other light beams, other electrical signals, and/or other electro-optic modulation systems.

A first modulated light pulse is formed using the modulation system 220 (410). The first modulated light pulse is formed by causing a first light pulse 306_1 to be incident on the material 122 and by applying a first voltage pulse 325a_1 to the material 122 at time t1 . At time t1 , the first light pulse 306_1 is incident on the material 122 and the modulation system 220 is in the ON state. Thus, the portion of the first light pulse 306_1 , starting at time t1 and through the duration 331_1 , passes through the material 122 to become the first modulated light pulse. Also, application of the first voltage pulse 325a_1 causes sound waves to propagate within the material 122 . This sound wave is referred to as the first sound wave, and it may continue to propagate within the material 122 after the first voltage pulse 325a_1 has ended and the modulation system 220 is in the OFF state.

An intermediate voltage pulse 325b_1 is applied to the material 122 (420). Applying the intermediate voltage 325b_1 to the material 122 also causes a sound wave (called a second sound wave) to propagate within the material 122 . The second sound wave interferes with the first sound wave. Constructive interference increases the amplitude of a sound wave, and destructive interference decreases the amplitude of the sound wave. The amplitude and/or duration 332 of the intermediate voltage pulse 325b_1 determines the amplitude of the second sound wave. Delay 330 determines the phase of the second sound wave relative to the first sound wave. Thus, by controlling the delay 330 and/or the amplitude B, the nature of the interaction between the first sound wave and the second sound wave can be controlled. For example, if the second sound wave has the same amplitude and opposite phase as the first sound wave, the first and second sound waves are such that the sound wave does not propagate within the material 122 after the intermediate electrical pulse 325b_1 is applied. interfere

A second modulated light pulse is formed using modulation system 220 (430). A second modulated light pulse is formed after application of the intermediate voltage pulse 325b_1 to the material 122 . A second light pulse 306_2 is incident on the material 122 . At time t2, a second voltage pulse 325a_2 is incident on the material 122 to transition the modulation system 220 to the ON state. A portion of the second light pulse 306_2 , starting at time t2 and passing through a duration 331_2 , is transmitted through the material 122 .

As discussed above, the first sound wave and the second sound wave interfere, and the properties of the sound wave in the material 122 depend on the nature of the interference. The sound wave causes a deformation within the material 122, which changes the refractive index of the material 122, and by this change in refractive index, the light causes the modulation system 220 to leak as light when the modulation system 220 is in the OFF state. 220) can pass. The intermediate voltage pulse 325b_1 is used to change one or more characteristics of the second light pulse 306_2 in a desired manner. For example, the intermediate voltage pulse 325b_1 may be used to alter the maximum or average intensity, temporal duration, and/or temporal profile of the second optical pulse 306_2 . In some implementations, the intermediate voltage pulse 325b_1 is used to control and/or form the pedestal portion.

For example, depending on the nature of the sound wave in material 122, material 122 before time t2 or at a time after which voltage pulse 325a_2 is no longer applied (when modulation system 220 is in the OFF state). A portion of the light of the second light pulse 306_2 incident on the image may pass through the modulation system 220 as a light leak to form a pedestal portion on the second modulated light pulse. The strength, duration, and other properties of the pedestal depend on the amount of light leakage, which is controllable by tuning the sound waves within the material 122 . The sound waves in the material 122 may be controlled, adjusted, or mitigated by applying an intermediate voltage pulse 325b_1 to the material 122 . Accordingly, one or more characteristics of the pedestal portion are controlled or adjusted by applying the intermediate voltage pulse 325b_1. Also, one or more characteristics of the main portion of the light pulse 306_2 may be controlled with the intermediate voltage pulse 325b_1 .

The intermediate voltage pulse 325b_1 may be used to otherwise control one or more characteristics of the second optical pulse 306_2 . For example, as described above, the pedestal portion may be separated in time from the main portion of the modulated pulse. In these implementations, the intermediate voltage pulse 325b_1 may be used to alter separate pedestal portions and/or main portions.

Further, light beam 306 may include additional light pulses and electrical signal 324 may include additional voltage pulses. In some implementations, the control system 175 provides an indication of the amount of EUV light generated by the interaction between the target material 118 and the modulated light pulse as measured by the EUV sensor 184 ( FIG. 1 ). receive For example, a measured amount of EUV light is tracked over two or more interactions while varying the characteristics of the intermediate voltage pulse to determine the optimal setting of the intermediate voltage pulse. Delay 330 may be changed for each of several interactions to determine which delay 330 generates the most EUV light. In another example, the amplitude B of the intermediate voltage pulse 325b_1 is changed to determine the amplitude B that generates the most EUV light.

In some implementations, a lookup table or database is stored in electronic storage 178 that correlates optimal values of amplitude B, width 332 , and/or delay 330 with repetition rates of pulses in light beam 306 . Thus, amplitude B and/or delay 330 may change when the repetition rate of light beam 306 changes.

5 and 6 relate to a lithographic apparatus in which a modulation system such as systems 120 and 220 may be used. 5 is a block diagram of a lithographic apparatus 500 including a source collector module SO. This lithographic apparatus 500 includes:

- an illumination system (illuminator) IL configured to condition the radiation beam B (eg EUV radiation);

- a support structure (eg mask table) MT configured to support a patterning device (eg mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device ;

a substrate table (eg, wafer table) WT configured to hold a substrate (eg, a resist coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate; and

A projection system (eg, including one or more dies) configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (eg, comprising one or more dies) of the substrate W , reflective projection system) (PS).

An illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components for directing, shaping, or controlling radiation, or any combination thereof. .

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as, for example, whether the patterning device is maintained in a vacuum environment. . The support structure may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or table that is fixed or movable as needed. The support structure may ensure that the patterning device is in a desired position relative to the projection system, for example.

The term “patterning device” should be interpreted broadly to refer to any device that can be used to impart a radiation beam having a pattern in its cross-section to create a pattern in, for example, a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer of a device being created in the target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples of patterning devices include a mask, a programmable mirror array, and a programmable LCD panel. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. One embodiment of a programmable mirror array uses a matrix arrangement of miniature mirrors, each of which can be individually tilted to reflect an incoming radiation beam in a different direction. The tilted mirror imparts a pattern to the radiation beam, which is reflected by the mirror matrix.

Like the illumination system IL, the projection system PS may contain refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any of these, depending on the exposure radiation used or other factors such as the use of a vacuum. It may include various types of optical components such as combinations. For EUV radiation, it may be desirable to use a vacuum as other gases may absorb too much of the radiation. A vacuum environment can thus be provided throughout the entire beam path using vacuum walls and vacuum pumps.

5 and 6, the apparatus is of the reflective type (eg, using a reflective mask). This lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such "multi-stage" machines, additional tables can be used in parallel, or preliminary steps can be executed on one or more tables while one or more other tables are being used for exposure.

Referring to FIG. 5 , the illuminator IL receives the EUV radiation beam from the source collector module SO. A method of generating EUV light includes, but is not limited to, converting a material having at least one element, such as xenon, lithium, or tin, into a plasma state having one or more bright lines in the EUV range. In one of these methods, often referred to as a laser-generated plasma (“LPP”), the desired plasma is created by irradiating a fuel, such as droplets, stream, or clusters, of material with the desired prior-emitting element with a laser beam. The source collector module SO may be part of an EUV radiation system that includes a laser (not shown in FIG. 5 ) for providing a laser beam to excite the fuel. The resulting plasma emits output radiation, for example EUV radiation, which is collected using a radiation collector disposed in a source collector module. _{For example, where a carbon dioxide (CO 2} ) laser is used to provide a laser beam for fuel excitation, the laser and source collector module may be separate entities.

In this case, the laser is not considered to form part of the lithographic apparatus and the radiation beam travels from the laser to the source collector module using, for example, a beam delivery system comprising suitable directing mirrors and/or beam expanders. do. In other cases, the source may be an integral part of the source collector module, for example if the source is a discharge generating plasma EUV generator, sometimes referred to as a DPP source.

The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. In general, at least an outer radial dimension and/or an inner radial dimension (commonly referred to as σouter and σinside, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. The illuminator IL may also include various other components such as polyhedral field and pupil mirror devices. The illuminator IL may be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

The radiation beam B is incident on a patterning device (eg mask) MA held on a support structure (eg mask table) MT and is patterned by the patterning device. After being reflected from the patterning device (eg mask) MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. Using the second positioner PW and the position sensor PS2 (eg an interference device, linear encoder or capacitive sensor), the substrate table WT is, for example, in the path of the radiation beam B. It can be precisely moved to position different target parts C. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (eg mask) MA with respect to the path of the radiation beam B. Patterning device (eg, mask) MA and substrate W may be aligned using patterning device alignment marks M1 , M2 and substrate alignment marks P1 , P2 .

The illustrated device can be used in at least one of the following modes:

In step mode, the support structure (eg mask table) MT and substrate table WT are held essentially stationary, and the entire pattern imparted to the radiation beam is applied at once (ie in a single static exposure). It is projected onto the target part (C). The substrate table WT is then moved in the X direction and/or the Y direction to expose different target portions C. As shown in FIG.

In the scan mode, the support structure (eg mask table) MT and the substrate table WT are simultaneously projected (ie a single dynamic exposure) on the target portion C a pattern imparted with a radiation beam. are scanned The speed and direction of the substrate table WT relative to the support structure (eg mask table) MT may be determined by the (reduced) magnification and image reversal characteristics of the projection system PS.

In another mode, the support structure (eg, mask table) MT holds the programmable patterning device and remains essentially stationary, and the substrate table WT has a pattern imparted to the radiation beam onto the target portion C ) is moved or scanned while projected onto the image. In this mode, typically a pulsed radiation source is used, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between successive radiation pulses being scanned. This mode of operation can be readily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array of the type mentioned above.

Combinations and/or variations of the aforementioned modes of use or entirely different modes of use may be used.

6 shows in more detail one implementation of a lithographic apparatus 500 comprising a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment is maintained within the enclosure structure 620 of the source collector module SO. The systems IL, PS are likewise maintained in their own vacuum environment. The EUV radiation emitting plasma 2 may be formed by a laser-generated LPP plasma source. The function of the source collector module SO is to deliver the EUV radiation beam 20 from the plasma 2 so that it is focused on a virtual source point. The virtual source point is generally referred to as the intermediate focal point (IF), and the source collector module is positioned such that the intermediate focal point (IF) is located at or near the opening 621 in the enclosure structure 620 . The virtual source point IF is an image of the radiation emitting plasma 2 .

Radiation from the opening 621 of the intermediate focal point IF traverses the illumination system IL comprising, in this embodiment, a multifaceted field mirror device 22 and a multifaceted pupil mirror device 24 . These arrangements form a so-called "fly-eye" illuminator, which is shown by reference numeral 660 as well as the desired angular distribution of the radiation beam 21 in the patterning device MA as well as the desired uniformity of the radiation intensity of the patterning device MA. ) is arranged to provide When the radiation beam 21 is reflected from the patterning device MA held by the support structure (mask table) MT, a patterned beam 26 is formed, which patterned beam 26 is applied to the substrate table WT. ) is imaged by the projection system PS via the reflective elements 28 , 30 on the substrate W held by the . To expose the target portion C on the substrate W, the substrate table WT and the patterning device table MT perform synchronized movement to scan the pattern on the patterning device MA through a slit of illumination. A pulse of radiation is generated.

Each system IL, PS is disposed in its own vacuum or near-vacuum environment formed by an enclosure structure similar to enclosure structure 620 . More elements than shown may be present in illumination system IL and projection system PS in general. Also, there may be more mirrors than shown. There may be 1 to 6 additional reflective elements in addition to those shown in FIG. 6 , for example in the illumination system IL and/or the projection system PS.

Considering the source collector module SO in more detail, a laser energy source comprising a laser 623 is arranged to dispense laser energy 624 into a fuel comprising a target material. The target material may be any material that emits EUV radiation in a plasma state, such as xenon (Xe), tin (Sn), or lithium (Li). The plasma 2 is a highly ionized plasma having an electron temperature of several tens of electron volts (eV). Higher energy EUV radiation can be produced using other fuel materials, such as terbium (Tb) and gadolinium (Gd). Energy radiation generated during de-excitation and recombination of these ions is emitted from the plasma, is collected by an incident collector 3 close to normal, and is focused on an opening 621 . The plasma 2 and the opening 621 are located at the first and second focal points of the collector CO, respectively.

The collector 3 shown in FIG. 6 is a single curved mirror, although the collector may take other forms. For example, the collector may be a Schwarzschild collector with two radiation collecting surfaces. In one embodiment, the collector may be a grazing incidence collector comprising a plurality of substantially cylindrical reflectors superimposed on one another.

A droplet generator 626 disposed within the enclosure structure 620 is arranged to fire a high frequency stream 628 of droplets towards the plasma 2 at a desired location to deliver a fuel, eg, liquid tin. Droplet generator 626 may be target forming apparatus 216 and/or include an adhesive, such as adhesive 234 . In operation, laser energy 624 is delivered in synchronization with the operation of droplet generator 626 to deliver an impulse of radiation to convert each fuel droplet into plasma 2 . The droplet propagation frequency may be several kilohertz, for example 50 kHz. In practice, laser energy 624 is delivered in at least two pulses: a pre-pulse with limited energy is delivered to the droplet before it reaches the plasma position, vaporizing the fuel material into a small cloud. and then a main pulse of laser energy 624 is delivered to this cloud at a desired location to generate plasma 2 . A trap 630 is provided on the opposite side of the enclosure structure 620 to trap fuel that has not been converted to plasma for any reason.

Droplet generator 626 includes a reservoir 601 containing a fuel liquid (eg, molten tin), a filter 669 , and a nozzle 602 . The nozzle 602 is configured to eject the liquid of the fuel liquid towards the plasma 2 formation position. Droplets of fuel liquid may be ejected from nozzle 602 by a combination of pressure in reservoir 601 and vibration applied to the nozzle by a piezoelectric actuator (not shown).

As will be appreciated by those skilled in the art, reference axes X, Y, Z can be defined to measure and describe the geometry and behavior of the device, its various components, and the radiation beams 20, 21, 26. have. For each part of the device, local frames of reference in the X, Y and Z axes can be defined. In the example of FIG. 6 , the Z axis generally coincides with the direction of the optical axis O at a given point in the system and is generally perpendicular to the plane of the patterning device (reticle) MA and the plane of the substrate W. In the source collector module, the X axis generally coincides with the direction of fuel flow 628 , and the Y axis is orthogonal thereto and points out of the ground as indicated in FIG. 6 . On the other hand, in the vicinity of the support structure MT holding the reticle MA, the X axis is generally transverse to the scanning direction aligned with the Y axis. For convenience, in this region of FIG. 6, which is a schematic diagram, the X axis points outward from the ground as indicated. Such markings are customary in the art and are employed herein for convenience. In principle, any frame of reference can be chosen to describe the device and its behavior.

There are many additional components in a typical apparatus that are not shown here but are used in the overall operation of the source collector module and lithographic apparatus 500 . These include arrangements to reduce or mitigate the effects of contamination in the enclosed vacuum, for example to prevent the deposition of fuel material impairing the performance of the collector 3 and other optics. Other features that are present but not described in detail are all sensors, controllers, and actuators involved in the control of the various components and subsystems of the lithographic apparatus 500 .

Referring to FIG. 7 , an implementation form of the LPP EUV light source 700 is shown. This light source 700 can be used as the source collector module SO of the lithographic apparatus 500 . Also, the optical pulse generation system 104 of FIG. 1 may be part of the drive laser 715 . Drive laser 715 may be used as laser 623 ( FIG. 6 ).

The LPP EUV light source 700 is formed by irradiating the target mixture 714 at the plasma formation location 705 with an amplified light beam 710 that travels along the beam path to the target mixture 714 . The target material discussed in connection with FIGS. 1 , 2A, 2B, and 3 , and the target in flow 121 discussed in connection with FIG. 1 may be or include the target mixture 714 . Plasma formation location 705 is within interior 707 of vacuum chamber 730 . When the amplified light beam 710 impinges on the target mixture 714 , the target material in the target mixture 714 is converted to a plasma state with elements having bright lines in the EUV range. The generated plasma has certain properties that depend on the composition of the target material in the target mixture 714 . These characteristics may include the wavelength of EUV light produced by the plasma and the type and amount of debris emitted from the plasma.

The light source 700 is also a supply system 725 that delivers, controls, and directs a target mixture 714 in the form of droplets, liquid streams, solid particles or clusters, solid particles contained within droplets, or solid particles contained within a liquid stream. includes Target mixture 714 includes a target material such as, for example, water, tin, lithium, xenon, or any material that has a bright line in the EUV range when converted to a plasma state. For example, elemental tin is pure tin (Sn); tin compounds such as SnBr ₄ , SnBr ₂ , SnH ₄ ; a tin alloy, such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys. The target mixture 714 may include impurities such as non-target particles. Accordingly, in the absence of impurities, the target mixture 714 is composed of only the target material. The target mixture 714 is delivered by a supply system 725 to the interior 707 of the chamber 730 and to the plasma formation location 705 .

The light source 700 includes a drive laser system 715 that generates an amplified light beam 710 due to a population inversion within the gain medium or gain media of the laser system 715 . The light source 700 includes a beam delivery system between the laser system 715 and the plasma forming location 705 , which includes a beam delivery system 720 and a focus assembly 722 . The beam transport system 720 receives the amplified light beam 710 from the laser system 715, steers and modifies the amplified light beam 710 as needed, and directs the amplified light beam 710 to the focus assembly ( 722). The focus assembly 722 receives the amplified light beam 710 and focuses the beam 710 to the plasma formation location 705 .

In some implementations, laser system 715 may include one or more optical amplifiers, lasers, and/or lamps to provide one or more main pulses and optionally one or more pre-pulses. In implementations that include one or more pre-pulses, an optical pulse generation system, such as optical pulse generation system 104 , may be disposed in one or more paths of the pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength with high gain, an excitation source, and internal optics. The optical amplifier may or may not have a laser mirror, or other feedback device that forms a laser cavity. Thus, the laser system 715 produces an amplified light beam 710 due to the density inversion of the gain medium of the laser amplifier even in the absence of a laser cavity. In addition, the laser system 715 can provide an amplified light beam 710 that is a coherent laser beam when there is a laser cavity to provide sufficient feedback to the laser system 715 . The term “amplified light beam” refers to one or more of light from laser system 715 that is only amplified but not necessarily coherent laser oscillation and light from laser system 715 that is amplified and also coherent laser oscillation. include

The optical amplifier in the laser system 715 may _{include a fill gas comprising CO 2} as a gain medium and amplify light at a wavelength of about 9100 to about 11000 nm, particularly about 10600 nm, at a gain of 800 times or greater. have. Amplifiers and lasers suitable for use in the laser system 715 are about, for example, operating at relatively high powers of 10 kW or greater and with high pulse repetition rates of, for example, 40 kHz or greater, using DC or RF excitation. a pulsed laser device that produces radiation of 9300 nm or about 10600 nm, for example a pulsed gas discharge CO ₂ laser device. The pulse repetition rate may be, for example, 50 kHz. The optical amplifier in the laser system 715 may include a cooling system such as water that may be used when operating the laser system 715 at high power.

The light source 700 includes a collector mirror 735 having an opening 740 through which the amplified light beam 710 can reach the plasma formation location 705 . Collector mirror 735 may be, for example, an elliptical mirror having a primary focus at plasma formation position 705 and a secondary focus at intermediate position 745 (also called intermediate focus), where EUV light is 700), and may be input to, for example, an integrated circuit lithography tool (not shown). The light source 700 is also configured to reduce the amount of plasma generating debris entering the focus assembly 722 and/or the beam transport system 720 while allowing the amplified light beam 710 to reach the plasma forming location 705 . It may include a hollow conical shroud 750 with an open end that tapers from the collector mirror 735 toward the plasma formation location 705 . For this purpose, a gas flow may be provided in the shroud that is directed towards the plasma formation location 705 .

Light source 700 may also include a main controller 755 coupled to droplet position detection feedback system 756 , laser control system 757 , and beam control system 758 . The light source 700 provides, for example, an output indicative of the position of the droplet with respect to the plasma formation location 705 , and uses this output to calculate a droplet position error, for example, per droplet or on average. one or more targets or droplet imagers 760 to provide a drop position detection feedback system 756 capable of calculating position and trajectory. Accordingly, the drop position detection feedback system 756 provides the drop position error as an input to the main controller 755 . Accordingly, the main controller 755 may provide laser position, direction, and timing correction signals to, for example, a laser control system 757 that may be used to control a laser timing circuit and/or chamber 730 . to the beam control system 758 for controlling the amplified light beam position and shaping of the beam transport system 720 to vary the position and/or focus power of the beam focus within the .

The supply system 725 includes a target material delivery control system 726 , which operates in response to a signal from the main controller 755 , to errone the droplet reaching the desired plasma formation location 705 . The ejection point of the droplet ejected by the target material supply device 727 may be modified to correct for . The target material supply device 727 includes a target forming device that uses an adhesive, such as an adhesive 234 .

The light source 700 also includes, but is not limited to, pulse energy, an energy distribution as a function of wavelength, energy within a particular band of wavelength, energy outside of a particular band of wavelength, and an angular distribution and/or average power of EUV intensity. optical detectors 765 , 770 for measuring one or more EUV optical parameters, but not limited to . The light source detector 765 generates a feedback signal for use by the main controller 755 . The feedback signal may represent errors in parameters such as, for example, the timing and focus of the laser pulse to properly capture the droplet at the right place and time for effective and efficient EUV light generation.

The light source 700 may include a guide laser 775 that may be used to align various portions of the light source 700 or to assist in steering the amplified light beam 710 to the plasma formation location 705 . With respect to the guide laser 175 , the light source 700 includes a metrology system 724 disposed within the focus assembly 722 for sampling a portion of the light from the guide laser 175 and the amplified light beam 710 . In another implementation, metrology system 724 is disposed within beam transport system 720 . Metrology system 724 may include optical elements that sample or redirect a subset of light, such optical elements made of any material capable of withstanding the power of the guide laser beam and the amplified light beam 710 . A beam analysis system is formed from metrology system 724 and a main controller 755 , which analyzes the sampled light from guide laser 775 and uses this information to control beam control system 758 . This is because the components in the focus assembly 722 are adjusted through the

Accordingly, in summary, the light source 700 generates an amplified light beam 710 , which is directed along a beam path to irradiate the target mixture 714 at a plasma formation location 705 to cause the mixture 714 . It converts the target material within the plasma into a plasma that emits light in the EUV range. The amplified light beam 710 operates at a specific wavelength (also referred to as the driving laser wavelength) that is determined based on the design and characteristics of the laser system 715 . In addition, the amplified light beam 710 provides suitable optical feedback for the target material to provide sufficient feedback to the laser system 715 to generate coherent laser light or for the drive laser system 715 to form the laser cavity. It may be a laser beam when including.

The implementation can be further described by the following clauses:

1. A device for an extreme ultraviolet (EUV) light source, comprising:

The device is:

a light modulation system comprising an electro-optic material, the light modulation system configured to receive a pulsed light beam comprising a plurality of light pulses separated in time from one another; and

A second electric pulse is applied to the electro-optic material while a second light pulse is incident on the electro-optic material, such that a first electric pulse is applied to the electro-optic material while the first light pulse is incident on the electro-optic modulator. and control the power source such that after the first light pulse is incident on the electro-optic material an intermediate electric pulse is applied to the electro-optic material before the second light pulse is incident on the electro-optic material. A device for an extreme ultraviolet (EUV) light source comprising a control system.

2. The method of clause 1, wherein applying the first electrical pulse to the electro-optic material induces a physical effect in the electro-optic material, wherein the physical effect occurs when the intermediate electrical pulse is applied to the electro-optic material. , present in the electro-optic material, for an extreme ultraviolet (EUV) light source.

3. Apparatus for an extreme ultraviolet (EUV) light source according to clause 2, wherein the physical effect comprises acoustic waves and/or mechanical strain traveling within the electro-optic material.

4. The apparatus of clause 2, wherein the application of the intermediate electrical pulse to the electro-optic material reduces the physical effect.

5. The apparatus for an extreme ultraviolet (EUV) light source according to clause 1, wherein the first light pulse and the second light pulse are continuous light pulses within the pulsed light beam.

6. The apparatus of clause 1, wherein the control system is configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse.

7. The apparatus of clause 1, wherein the electro-optic material comprises a semiconductor.

8. The apparatus of clause 1, wherein the electro-optic material comprises an insulator.

9. The apparatus of clause 1, wherein the electro-optic material comprises electro-optic crystals.

10. The apparatus of clause 1, wherein the apparatus for an extreme ultraviolet (EUV) light source further comprises at least one polarization-based optical element.

11. The apparatus of clause 1, wherein the intermediate electrical pulse generates an acoustic disturbance that interferes with the acoustic disturbance caused by the first electrical pulse.

12. A device for forming light pulses, comprising:

The device is:

A light modulation system comprising an electro-optic material, wherein the light modulation system is configured to transmit light in an ON state and block light in an OFF state, wherein the light modulation system comprises at least first and second optical pulses separated in time from each other. configured to receive a pulsed light beam comprising light pulses; and

a control system coupled to the voltage source;

The control system is:

by causing the voltage source to apply a first voltage pulse to the electro-optic modulator while the first light pulse is incident on the electro-optic modulator, wherein the first voltage pulse is configured to turn the electro-optic modulator into an ON state. to generate a first shaping light pulse;

to apply an intermediate electrical pulse to the electro-optic material; And

to generate a second shaping light pulse by applying a second voltage pulse to the electro-optic material after applying the first voltage pulse and the intermediate voltage pulse and while the second light pulse is incident on the electro-optic material; wherein the second voltage pulse is configured to switch the electro-optic modulator to the ON state, and wherein a characteristic of the second forming light pulse is controlled by applying the intermediate voltage pulse to the electro-optic material. forming device.

13. The method according to clause 12, wherein the second forming light pulse comprises a pedestal portion and a main portion, and the property of the second forming light pulse is such that the property of the pedestal portion is in the electro-optic material with the intermediate portion. and a characteristic of the pedestal to be controlled by applying a voltage pulse.

14. The apparatus of clause 13, wherein the pedestal portion and the main portion are temporally continuous.

15. The apparatus of clause 13, wherein the characteristics of the pedestal portion include a temporal duration, a maximum intensity, and/or an average intensity of the pedestal portion.

16. The apparatus of clause 12, wherein applying the intermediate voltage pulse to the electro-optic material alters optical leakage light transmitted through the optical modulation system in the OFF state.

17. The apparatus of clause 16, wherein applying the intermediate voltage pulse to the electro-optic material reduces optical leakage light transmitted through the optical modulation system in the OFF state.

18. As in section 12,

the first voltage pulse is applied to the electro-optic material at a first time by the control system;

the intermediate voltage pulse is applied to the electro-optic material at a second time after the first time by the control system;

the second time and the first time are temporally separated by a delay time,

and the control system is further configured to adjust the delay time to control a characteristic of the second formed light pulse.

19. The apparatus of clause 18, wherein the control system is further configured to control at least one of an amplitude, a temporal duration, and a phase of the intermediate voltage pulse.

20. Clause 13,

The control system is:

to receive an indication of a measured characteristic of the pedestal portion, and

and adjust a characteristic of the intermediate voltage pulse based on the received indication.

21. As in section 12,

The control system is:

receive an indication of an amount of extreme ultraviolet (EUV) light generated by the plasma; and

and adjust a characteristic of the intermediate voltage pulse based on a received indication of an amount of EUV light.

22. The clause 21,

wherein the control system is configured to adjust a characteristic of the intermediate voltage pulse such that the control system adjusts an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a second time wherein the second time is a time at which the intermediate voltage pulse is applied to the electro-optic material.

23. A method of adjusting a characteristic of a pedestal of a light pulse, comprising:

The method is:

forming a first optical pulse comprising a first pedestal portion and a first main portion by applying a first voltage pulse to an electro-optic material of the light modulation system while light is incident on the light modulation system;

applying an intermediate voltage pulse to the electro-optic material after applying the first voltage pulse; and

forming a second light pulse by applying a second voltage pulse to the electro-optic material after the first voltage pulse and the intermediate voltage pulse and while light is incident on the electro-optic material; wherein the characteristic of is adjusted based on the application of the intermediate voltage pulse.

24. The method of clause 23, wherein the method comprises:

amplifying the first optical pulse to form an amplified first optical pulse;

receiving an indication of an amount of extreme ultraviolet (EUV) light emitted from a plasma generated by interacting the amplified first pulse of light with a target material; and

and determining at least one characteristic of the intermediate voltage pulse based on a received indication of an amount of EUV light emitted from the plasma.

25. The method of clause 23, wherein the at least one characteristic of the intermediate voltage pulse comprises a time delay after application of the first voltage pulse, and wherein determining the at least one characteristic of the intermediate voltage pulse is emitted from the plasma. and determining the time delay based on a received indication of an amount of EUV light.

26. The intermediate voltage pulse of clause 24, wherein the at least one characteristic of the intermediate voltage pulse comprises an amplitude and/or a duration of the intermediate voltage pulse, and wherein determining the at least one characteristic of the intermediate voltage pulse comprises the intermediate voltage pulse. A method of adjusting a characteristic of a light pulse comprising determining the amplitude and/or duration of

27. The method of clause 23, wherein the second optical pulse comprises a pedestal portion and a main portion, wherein a characteristic of the pedestal portion is adjusted based on application of the intermediate voltage pulse.

28. The method of clause 27, wherein the pedestal portion is temporally continuous with the main portion.

29. An extreme ultraviolet (EUV) light source comprising:

Vessel;

a target material supply device configured to be coupled to the container;

a light modulation system configured to be positioned to receive a pulsed light beam, the light modulation system comprising an electro-optic material; and

a control system coupled to the voltage source;

The control system is:

cause the voltage source to apply a plurality of forming voltage pulses to the electro-optic material, each of the plurality of forming voltage pulses being applied to the electro-optic material at a different time, and

the voltage source applies at least one intermediate voltage pulse to the electro-optic material, wherein the at least one intermediate voltage pulse is applied to the electro-optic material between two successive forming voltage pulses of the plurality of forming voltage pulses; An extreme ultraviolet (EUV) light source.

30. The method of clause 29, wherein the target material supply device is configured to provide a plurality of target material droplets to a target area within the vessel, the target material droplets arriving at the target area at a target delivery rate, the control and the system applies the forming voltage pulses to the electro-optic material at a formation rate that is dependent on the target delivery rate.

31. The characteristic of clause 28, wherein the characteristics of the intermediate voltage pulse include amplitude and/or phase;

The control system is:

to access a stored amplitude and/or phase in relation to the rate of formation; and

and cause the voltage source to generate the intermediate voltage pulse with an accessed amplitude and/or phase.

32. of clause 29,

and the control system is further configured to control a time delay between application of one of the forming voltage pulses and one of the intermediate voltage pulses.

33. The method of clause 29, wherein the extreme ultraviolet (EUV) light source further comprises an optical amplifier,

here,

a light pulse is formed whenever a forming voltage pulse is applied to the electro-optic material;

the formed optical pulse is amplified by the optical amplifier to form an amplified optical pulse;

the control system is further configured to be coupled to a metrology system configured to measure an amount of EUV light generated by the plasma within the vessel;

the plasma is formed by irradiating the target material with the formed amplified light pulse;

the control system is configured to receive a measured amount of EUV light from the metrology system;

and the control system is configured to change one or more characteristics of the intermediate voltage pulse based on the measured amount of EUV light.

34. The intermediate voltage pulse of clause 33, wherein one or more characteristics of the intermediate voltage pulse are an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or of a most recently formed voltage pulse An extreme ultraviolet (EUV) light source, including a delay time after application.

Other implementations are within the scope of the claims.

Claims (34)

A device for an extreme ultraviolet (EUV) light source, comprising:
The device is:
a light modulation system comprising an electro-optic material, the light modulation system configured to receive a pulsed light beam comprising a plurality of light pulses separated in time from one another; and
A second electric pulse is applied to the electro-optic material while a second light pulse is incident on the electro-optic material, such that a first electric pulse is applied to the electro-optic material while the first light pulse is incident on the electro-optic modulator. and control the power source such that after the first light pulse is incident on the electro-optic material an intermediate electric pulse is applied to the electro-optic material before the second light pulse is incident on the electro-optic material. A device for an extreme ultraviolet (EUV) light source comprising a control system. The method of claim 1,
applying the first electrical pulse to the electro-optic material causes a physical effect in the electro-optic material, the physical effect being in the electro-optic material when the intermediate electrical pulse is applied to the electro-optic material Devices for phosphorus, extreme ultraviolet (EUV) light sources. 3. The method of claim 2,
wherein the physical effect includes acoustic waves and/or mechanical strain traveling within the electro-optic material. 3. The method of claim 2,
wherein the physical effect is reduced by applying the intermediate electrical pulse to the electro-optic material. The method of claim 1,
wherein the first light pulse and the second light pulse are continuous light pulses within the pulsed light beam. The method of claim 1,
and the control system is configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse. The method of claim 1,
wherein the electro-optic material comprises a semiconductor. The method of claim 1,
and the electro-optic material comprises an insulator. The method of claim 1,
wherein the electro-optic material comprises an electro-optic crystal. The method of claim 1,
wherein the device for an extreme ultraviolet (EUV) light source further comprises at least one polarization-based optical element. The method of claim 1,
wherein the intermediate electrical pulse generates an acoustic disturbance that interferes with the acoustic disturbance caused by the first electrical pulse. A device for forming light pulses comprising:
The device is:
A light modulation system comprising an electro-optic material, wherein the light modulation system is configured to transmit light in an ON state and block light in an OFF state, wherein the light modulation system comprises at least first and second optical pulses separated in time from each other. configured to receive a pulsed light beam comprising light pulses; and
a control system coupled to the voltage source;
The control system is:
by causing the voltage source to apply a first voltage pulse to the electro-optic modulator while the first optical pulse is incident on the electro-optic modulator, wherein the first voltage pulse is configured to turn the electro-optic modulator into an ON state. to generate a first shaping light pulse;
to apply an intermediate electrical pulse to the electro-optic material; And
to generate a second shaping light pulse by applying a second voltage pulse to the electro-optic material after applying the first voltage pulse and the intermediate voltage pulse and while the second light pulse is incident on the electro-optic material; wherein the second voltage pulse is configured to switch the electro-optic modulator to the ON state, and wherein a characteristic of the second forming light pulse is controlled by applying the intermediate voltage pulse to the electro-optic material. forming device. 13. The method of claim 12,
wherein the second forming light pulse includes a pedestal portion and a main portion, wherein a characteristic of the second forming light pulse is such that a characteristic of the pedestal portion is controlled by applying the intermediate voltage pulse to the electro-optic material. A device for forming light pulses, comprising the characteristics of a pedestal. 14. The method of claim 13,
wherein the pedestal portion and the main portion are temporally continuous. 14. The method of claim 13,
wherein the characteristics of the pedestal portion include a temporal duration, a maximum intensity, and/or an average intensity of the pedestal portion. 13. The method of claim 12,
and applying the intermediate voltage pulse to the electro-optic material changes the amount of optical leakage light transmitted through the optical modulation system in the OFF state. 17. The method of claim 16,
and applying the intermediate voltage pulse to the electro-optic material reduces optical leakage light transmitted through the optical modulation system in the OFF state. 13. The method of claim 12,
the first voltage pulse is applied to the electro-optic material at a first time by the control system;
the intermediate voltage pulse is applied to the electro-optic material at a second time after the first time by the control system;
the second time and the first time are temporally separated by a delay time,
and the control system is further configured to adjust the delay time to control a characteristic of the second formed light pulse. 19. The method of claim 18,
and the control system is further configured to control at least one of an amplitude, a temporal duration, and a phase of the intermediate voltage pulse. 14. The method of claim 13,
The control system is:
to receive an indication of a measured characteristic of the pedestal portion, and
and adjust a characteristic of the intermediate voltage pulse based on the received indication. 13. The method of claim 12,
The control system is:
receive an indication of an amount of extreme ultraviolet (EUV) light generated by the plasma; and
and adjust a characteristic of the intermediate voltage pulse based on a received indication of an amount of EUV light. 22. The method of claim 21,
wherein the control system is configured to adjust a characteristic of the intermediate voltage pulse such that the control system adjusts an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a second time wherein the second time is a time at which the intermediate voltage pulse is applied to the electro-optic material. A method of adjusting the properties of a light pulse, comprising:
The method is:
forming a first light pulse by applying a first voltage pulse to an electro-optic material of the light modulation system while light is incident on the light modulation system;
applying an intermediate voltage pulse to the electro-optic material after applying the first voltage pulse; and
forming a second light pulse by applying a second voltage pulse to the electro-optic material after the first voltage pulse and the intermediate voltage pulse and while light is incident on the electro-optic material; wherein the characteristic of the pulse is based on application of the intermediate voltage pulse. 24. The method of claim 23,
The method is:
amplifying the first optical pulse to form an amplified first optical pulse;
receiving an indication of an amount of extreme ultraviolet (EUV) light emitted from a plasma generated by interacting the amplified first pulse of light with a target material; and
and determining at least one characteristic of the intermediate voltage pulse based on a received indication of an amount of EUV light emitted from the plasma. 24. The method of claim 23,
wherein the at least one characteristic of the intermediate voltage pulse comprises a time delay after application of the first voltage pulse, and wherein determining the at least one characteristic of the intermediate voltage pulse is dependent on a received indication of an amount of EUV light emitted from the plasma. determining the time delay based on the method. 25. The method of claim 24,
The at least one characteristic of the intermediate voltage pulse comprises an amplitude and/or duration of the intermediate voltage pulse, and determining the at least one characteristic of the intermediate voltage pulse comprises an amplitude and/or duration of the intermediate voltage pulse. A method of adjusting a property of an optical pulse comprising determining. 24. The method of claim 23,
wherein the second optical pulse includes a pedestal portion and a main portion, wherein a characteristic of the pedestal portion is adjusted based on application of the intermediate voltage pulse. 28. The method of claim 27,
wherein the pedestal portion is temporally continuous with the main portion. An extreme ultraviolet (EUV) light source comprising:
Vessel;
a target material supply device configured to be coupled to the container;
a light modulation system configured to be positioned to receive a pulsed light beam, the light modulation system comprising an electro-optic material; and
a control system coupled to the voltage source;
The control system is:
cause the voltage source to apply a plurality of forming voltage pulses to the electro-optic material, each of the plurality of forming voltage pulses being applied to the electro-optic material at a different time, and
the voltage source applies at least one intermediate voltage pulse to the electro-optic material, wherein the at least one intermediate voltage pulse is applied to the electro-optic material between two successive forming voltage pulses of the plurality of forming voltage pulses; An extreme ultraviolet (EUV) light source. 30. The method of claim 29,
the target material supply device is configured to provide a plurality of target material droplets to a target area within the vessel, the target material droplets arrive at the target area at a target delivery rate, the control system dependent on the target delivery rate An extreme ultraviolet (EUV) light source for applying the forming voltage pulses to the electro-optic material at a formation rate of 30. The method of claim 29,
the characteristics of the intermediate voltage pulse include amplitude and/or phase;
The control system is:
to access a stored amplitude and/or phase in relation to the rate of formation; and
and cause the voltage source to generate the intermediate voltage pulse with an accessed amplitude and/or phase. 30. The method of claim 29,
and the control system is further configured to control a time delay between application of one of the forming voltage pulses and one of the intermediate voltage pulses. 30. The method of claim 29,
The extreme ultraviolet (EUV) light source further comprises an optical amplifier,
here,
a light pulse is formed whenever a forming voltage pulse is applied to the electro-optic material;
the formed optical pulse is amplified by the optical amplifier to form an amplified optical pulse;
the control system is further configured to be coupled to a metrology system configured to measure an amount of EUV light generated by the plasma within the vessel;
the plasma is formed by irradiating the target material with the formed amplified light pulse;
the control system is configured to receive a measured amount of EUV light from the metrology system;
and the control system is configured to change one or more characteristics of the intermediate voltage pulse based on the measured amount of EUV light. 34. The method of claim 33,
The one or more characteristics of the intermediate voltage pulse include an amplitude of the intermediate voltage pulse, a temporal duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a delay time after application of a most recent forming voltage pulse. Extreme ultraviolet (EUV) light source.

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